Heavy duty pistons



Sept. 19, 1961 w. c. CHENEY ETAL 3,000,676

HEAVY DUTY PISTONS 2 Sheets-Sheet 1 Filed June 12, 1958 VENTORS Caz/v5) ATTORNEYS.

Sept. 19, 1961 w. c. CHENEY ETAL 3,000,676

HEAVY DUTY PISTONS Filed June 12, 1958 2 Sheets-Sheet 2 11144 0514 C (IVs/vs) 4 Mags/r414 61940217510,

HTTORN 5Y5.

HEAVY DUTY PESTONS Wendell C. Cheney, Lake City, Minn, and Marshall G. Whitfield, Garden City, N.Y.; said Wendell C. Cheney ass gnor, by mesne assignments, to Gould-National Batteries, inc, St. Paul, Minn, a corporation of Delaware Filed June 12, 1958, Ser. No. 741,563 Claims. (Cl. 309-14) This application is related to and is a continuationin-part of our copending application Serial No. 656,910 filed May 3, 1957, and entitled Piston for Internal Combustion Engines. In that application there is described a structure having a heavy metal head portion and a light metal body, there being wire reinforcements for the Wrist pin bosses attached to and extending downwardly from the end portion. Pistons of the type described in the said application have given an excellent account of themselves in heavy duty service. In diesel engines and the like, the head portion has prevented the cutting away of the light metal by the fuel injection blast. The head portion has contributed great strength to the piston; it has been designed in such a way as to hold to the light metal body; and the wire reinforcements for the wrist pin bosses have served also to anchor the head in place.

It will be understood that light metal pistons are subjected not only to very great physical stresses in heavy duty service, but also to thermal operating stresses due to heating and cooling cycles. It is well known that the strength of aluminum alloys diminishes as the temperature rises. The light metal piston as such has not proved satisfactory for heavy duty service. ture of pistons is a contributing factor. invariably actual failure is preceded by the start of a fracture. The fracture may start in one of the piston ring grooves, at an oil hole, at the end of a slot in a slot-type piston, or at the wrist pin boss. A fracture starting at the wrist pin boss is by far the most common type of failure, probably occurring in at least 90% of the cases. When the fracture starts at the pin boss, it is most often on the inside face of the boss at the top. It may, however, start in a rib or strut which ties the wrist pin boss to the skirt of the piston and to the head. In any event, a fracture once started develops progressively under the stresses of use, and tends to branch into Weak places in the piston. The fracture may enter the ring groove area and proceed circumferentially around the piston, freeing the head portion thereof from the body in a piston made entirely of light metal. Similarly, a fracture starting in or adjacent an unreinforced wrist pin boss may proceed across the wrist pin boss, ultimately freeing the connecting rod. When any of these things happen, the engine block is usually broken and destroyed.

These difficulties are not encountered in the piston of the said copending application. At the same time, it may be noted that the heavy metal head portion adds considerably to the weight and to the expense of the structure. It has been found that the reinforcement of the wrist pin bosses alone, as hereinafter set forth, contributes very greatly to the life of the light metal pistons in heavy duty service, irrespective of the presence or absence of the heavy metal head or cap. Further, it has been found that in pistons where both the head portion and the body are of light metal, it is readily possible to combine reinforcement means for the wrist pin bosses with means tending to prevent the separation of the body portion of the piston from the head portion, and thus not only minimize cracking in the area of the piston ring grooves but also render light metal pistons capable of heavy duty service.

The physical structheatre Patented Sept. 19, 1961 The attainment of the advantages set forth above constitutes an important object of the invention.

It is an object of the invention to provide a light piston which, while capable of heavy duty service, has a distinct Weight advantage over a piston of comparable size but having a heavy metal cap or head. I

It is an object of the invention to provide cheaply a light metal piston reinforced at those points where failure is likely to occur, which is simple to construct, and relatively low in price.

It is an object of the invention to provide means for tying the head portion to the body portion or skirt portron of an \all-light-metal piston, and a light metal piston which is reinforced at the primary area where fracture is likely to occur by means of relatively low mass, which means are wholly embedded in the light metal of the cast structure.

It is an object of the invention to provide reinforcing structures which are readily and accurately supported in a mold during the casting operation.

These and other objects of the invention, which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished by that structure and arrangement of parts of which certain exemplary embodiments will now be described.

Reference is made to the accompanying drawings wherein:

FIG. 1 is a vertical sectional view of an exemplary light metal piston showing reinforcements of one type falling within the scope of this invention, the section being taken in a vertical plane passing through the axis of the wrist pin bosses.

FIG. 2 is a sectional view of the same structure, the section being taken vertically and in a plane at right angles to the axis of the wrist pin bosses, and along the section line 2--2. I

FIG. 3 is a sectional view taken in the same fashion as that of FIG. 1 but showing another type of reinforcement.

FIG. 4 is a vertical sectional View of the same reinforced piston taken along the section line 44 of FIG. 3.

FIG. 5 is a vertical sectional view taken along a plane which includes the axis of the Wrist pin bosses, and showing yet another type of reinforcement.

FIG. 6 is a vertical sectional view of the same structure taken along the section line 6-6 of FIG. 5.

FIG. 7 is an elevational view of a type of wire reinforcement such as that employed in the structures of FIGS. 1 and 2.

FIG. 8 is a bottom view thereof.

FIG. 9 is a perspective view of a type of Wire reinforcement employed in the structure of FIGS. 3 and 4.

FIG. 10 is a perspective view of a type of wire reinforcement used in the structure of FIGS. 5 and 6.

FIG. 11 is a partial perspective view of a reinforcement member which may be employed for one or more of the piston ring grooves.

Referring to FIGS. 1 and 2, a light metal piston is shown having a head 1 and a skirt 3. Wrist pin bosses 5 and 7 are shown surrounding the wrist pin openings 8 and 9 as is usual in piston construction. While a particular shape of piston has been illustrated, it will be understood that the invention is applicable to pistons of other shapes and proportionalities. In the exemplary embodiment, the head of the piston is hollowed as at 10; and it may be provided with a hard metal head insert 11 in accordance with the teachings of Patent No. 2,775,493, issued December 25, 1956, in the name of Wendell C. Cheney.

The illustrated piston is provided with reinforcements.

These reinforcements are preferably made of drawn iron or steel wire, bent to formconvolutions 12 and 13, upwardly extending portions 1 transversely extending portions lying within the head and outwardly extending portions 16. The shape of the reinforcements will be more readily appreciated from FIGS. 7 and 8. The convolutions 12 surround the wrist pin openings and reinforce the Wrist pin bosses in depth. The transverse members 15 lie within the head of the piston and, being connected by the longitudinal portions 14', serve to anchor the head to the body of the piston. The entire wire reinforcement is embedded in the light metal of the piston as will be evident from FIGS. 1 and 2, excepting for the outer ends of the extensions 16. These ends serve to locate the reinforcement in a mold in which the light metal piston is cast, the outer ends, of the extensions 16 being thrust into holes in the mold or being clamped between separable parts thereof. When the completed cast piston is finished in the usual manner, as by being turned down to an exact cylindrical dimension, the projecting ends of the extensions 16 will be cut off ,flush with the turned surface of the light metal body.

At the time of the finishing of the light metal body, piston ring grooves, as indicated at 17, will be turned or milled therein. The use of the wrist pin boss and head reinforcement means thus far described does not preclude the use of other reinforcement means. Thus, one

or more of the ring grooves may be reinforced by any of the means hitherto employed for that purpose. A particularly desirable mode of reinforcement is indicated in Patent 2,793,923 in the names of Marshall G. Whitfield and Wendell C. Cheney, issued May 28, 1957. A wire reinforced groove is indicated at 18 in FIGS. 1 and 2; and a type of wire reinforcement for the purpose is indicated in FIG. 11 of this case. This reinforcement is made of iron, steel or bronze Wire so bent or configured as to provide outwardly extending bights 19, substantially parallel wire portions 20, and inwardly extending diverging bights 21. Wire reinforcements of the type shown in FIG. 11 may be made in long lengths and cut in such fashion that they may be bent in circular form and disposed in a piston mold at a position where a ring groove is to be cut. The outwardly extending bights 19 will, as taught in the said patent, be engaged in a groove in the mold. When the piston is turned to size and finished, these outwardly extending bights will be cut off. The milling or turning of the piston ring groove between the parallel portions 20 of the wire reinforcement will result in exposing parts of these parallel portions at the upper and lower faces of the groove to provide relatively closely spaced hard metal reinforcements for the groove in the position of wear. The inwardly extending bights 21 are embedded in the light metal of the piston, as will be evident from FIGS. 1 and 2, and constitute anchoring means.

Additional reinforcement means may be employed if desired, but are not usually necessary. Thus, as has hitherto been suggested in the art, a foraminous or mesh sleeve of heavy metal can be incorporated in the skirt of the piston. The use of the reinforcing means of this invention prevents or inhibits the formation of cracks in the wrist pin bosses and very greatly prolongs the heavy duty life of the structure. Furthermore, the tying of the wrist pin bosses to the head of the piston is effective in minimizing the propagation of failure cracks should they start, and in preventing the separation of the head of the piston from the body or skirt portion thereof even though cracks should be formed. While the size of the Wire is not a limitation on the invention, it may be pointed out that a drawn steel wire having a diameter of .090 in., at the temperature of operation of heavy duty pistons, will have from 4 to 6 times the strength of the same amount of aluminum alloy. The ductility of drawn wire is generally better than that of other forms of metal of like composition; and wire is generally'rnore economical in use. With wire reinforcements, it is easier to obtain sound castings without flaws. While other cross-section a1 shapes may be used, round wire presents less obstructions to the flow of the metal during casting.

It may be pointed out also that in View of the difference in the coefiicients of expansion between the light metal and the iron or steel wire, the wrist pin bosses and those parts of the light metal casting which are tied together with the wire constructions herein described, will be under compression which is a desirable condition.

In FIGS. 3 and 4, like parts have been given like index numerals. A modified form of reinforcement device for the wrist pin bosses and for tying the wrist pin bosses to the head has been indicated as comprising convolutions 22, risers 23 and 24,, and a pair of spaced transverse members 25 and 26 for each of the reinforcement devices. This specific structure is illustrated by itself in FIG. 9. Although this reinforcement is more expensive, it reinforces the wrist pin bosses to a greater extent in depth as will be evident, and it has additional engagement with the head of the piston to prevent separation. As previously described, this structure is also provided with lateral extensions 27 and 28, the outer ends of which can be located in the mold to position the reinforcement.

A simpler structure is illustrated in FIGS. 5 and 6 where, again, like parts have been given like index numerals. In the reinforcement convolutions 29 reinforce the wrist pin bosses in depth. Risers are provided, but the cross members within the head are omitted. Instead, the upper ends of the risers are turned outwardly at at 30 to provide locating means. The structure is illustrated by itself in FIG. 10 where the risers are indicated at 31 and 32.

Modifications of any of these structures may be made containing a greater number of convolutions for reinforcing the wrist pin bosses. As will be evident from the drawings, the wrist pin bosses are normally connected with the head by portions of the light metal which are thicker than adjacent portions of the body or the skirt. These thicker portions readily accommodate and permit the embedding of the vertically extending or riser portions of the reinforcement.

The term light metal is used herein to designate aluminum and alloys consisting preponderantly of aluminum. Without limiting the generality of the foregoing, an alloy of aluminum, silicon, nickel, copper, magnesium, vanadium, and antimony, as described in the now expired Patent 2,131,076 to Schwarz, is particularly useful for this type of service because it provides greater high temperature strength.

In the production of the structures of this invention, the matter of bond between the heavy metal and light metal portions is of reduced importance because the heavy metal parts which reinforce the wrist pin bosses are entirely embedded in the light metal. Nevertheless, a bond may be desired and may be provided in various ways. In one procedure the reinforcement, cleaned by sandblasting or otherwise, is electrically coated with tin to a thickness of about .0002 in. more or less. In the casting operation the mold is so constructed and the pouring is accomplished in such a way that the molten metal flows past the surfaces of the ferrous metal body against which it is cast for a substantial interval, carrying away oxides and impurities. In this procedure a sound bond is produced with a minimum of interface alloy and in many instances with no visible interface alloy. Such a procedure is taught in Patent 2,797,460, issued July 2, 1957, in the name of Marshall G. Whitfield.

In another procedure the cleaned surfaces of the reinforcement are coated with molybdenum or tungsten as by spraying or in other ways. After such coating the reinforcement may be dipped into a bath of molten aluminum or aluminum alloy prior to the casting of the light metal body against it, all as set forth in Patent 2,800,707, issued July 30, 1957, in the name of Marshall G. Whitfield. In that procedure an excellent bond is produced without the formation of any aluminum-iron interface alloy.

NIT

Yet again, if desired, the reinforcement after cleaning may be dipped into a bath of molten aluminum or aluminum alloy until coated thereby. The so coated part may be located in a mold and the light metal cast against it.

Modifications may be made in the invention without departing from the spirit of it. From the teachings herein, it will be clear that various forms of reinforcement, especially those which are produced by bending wire, may be made and that reinforcing structures may be attached together prior to location in a mold and the casting of the light metal. By way of example, a pair of structures such as those illustrated in FIGS. 7 and 8, may be located in a jig and their upper horizontal portions connected by one or more wire elements extending thereacross as at 33 in FIG. 1. However, such additional structures are not normally required since, as indicated, the greater part of the failure of light metal pistons in heavy duty usage occurs because of fractures starting at the wrist pin bosses.

The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. A light metal piston having a head portion and a skirt portion integral therewith, said skirt portion having inwardly extending wrist pin bosses, and heavy metal strand-like reinforcements embedded in said wrist pin bosses, each of said reinforcements having spaced convolutions the axis of which extends in the direction of the length of said wrist pin bosses.

2. The structure claimed in claim 1 in which said reinforcements are made of ferrous wire.

3. The structure claimed in claim 2 wherein one at least of the said convolutions of each reinforcement is prolonged upwardly so as to extend into the head of said light metal piston.

4. The structure claimed in claim 2 wherein one at least of the said convolutions of each reinforcement is prolonged upwardly so as to extend into the head of said light metal piston, and has a portion extending outwardly beyond said piston whereby said reinforcement may be located in a mold in which said light metal piston is cast.

5. The structure claimed in claim 3 wherein one at least of the convolutions of each reinforcement is prolonged upwardly to provide a bight in which vertical members extend into said head, said vertical members being connected by a transverse part embedded in said head and serving to anchor said head to said skirt.

6. The structure claimed in claim 3 wherein a plurality of the convolutions of said reinforcement extend upwardly forming closed loops, the top portions of which are embedded in the head of said light metal piston.

'7. The structure claimed in claim 5 wherein free ends of said wire reinforcements lying in the area of said convolutions extend outwardly in a direction substantially parallel to the axis of said convolutions so as to project beyond the area of said skirt and provide means whereby said reinforcements may be located in a mold during the casting of said light metal piston.

8. A reinforcement for the wrist pin boss of a light metal piston comprising a Wire member having spaced convolutions of a size to be embedded in a wrist pin boss, and an outwardly extending member whereby said reinforcement may be located in a mold.

9. The structure claimed in claim 8 wherein one at least of the said convolutions has an upwardly extending bight of a length such that the top of said bight may be embedded in the head portion of the said light metal piston.

10. A light metal piston comprising a head and a skirt, said skirt integral therewith having inwardly extending wrist pin bosses, and heavy metal reinforcement means for said wrist pin bosses, said reinforcing means each being formed of wire and having at least one portion extending into said head, at least one portion extending downwardly from said head, to a wrist pin boss and a portion having spaced convolutions for reinforcing said wrist pin boss in the direction of its length, said reinforcement being substantially wholly embedded within said light metal piston.

References Cited in the file of this patent UNITED STATES PATENTS 1,842,745 Butler Jan. 26, 1932 2,114,007 Wenzel Apr. 21, 1938 2,192,323 Moeller Mar. 5, 1940 2,267,724 Fahlman Dec. 30, 1941 2,426,732 Gates Sept. 2, 1947 

